1. Field of the Invention
The invention relates to an improved process for the production and purification of n-butyl acrylate.
2. Background Information and Description of Related Art
n-Butyl acrylate (BuAcA) is a commodity chemical useful for the production of acrylic resins and polymers and copolymers for paint formulations, solvent coatings, textile and leather finishes and adhesives and binders. One method of synthesizing BuAcA is to react n-butanol (BuOH) with acrylic acid (HAcA) in the presence of an acid catalyst, e.g., a sulfonic acid, in at least one reaction zone to produce a mixture of BuAcA, water and several by-product impurities, and subjecting the product mixture to purification in at least one distillation zone, together with any of various schemes of reflux and recycle streams among the reaction zone(s) and distillation zone(s) to obtain a BuAcA of relatively high purity. When any of these processes are operated, low boiling impurities produced in the reaction zone, i.e., those having boiling points near or below BuAcA, such as butyl acetate and dibutyl ether and characterized as "light ends", or "lights" must be systematically disposed of to prevent them from interfering with the described reaction and compromising the purity of the BuAcA. However, this is often difficult to accomplish, e.g. by purging an appropriate stream, without also losing an unduly large amount of BuAcA product and unreacted BuOH, and/or incurring an unfavorably large cost in energy consumption or purification equipment to prevent such loss. Thus, any improved process, which accomplishes an adequate disposal of light ends while keeping the loss of BuAcA and unreacted BuOH and/or the incremental cost of energy and equipment to a minimum, is very desirable.
U.S. Pat. No. 4,012,439, issued Mar. 15, 1977 to Erpenbach et al., discloses a process for producing n-butyl acrylate by reacting acrylic acid with n-butanol in liquid phase and in contact with an acid cation exchanger as a catalyst. The process utilizes a single reaction zone and three distillation zones.
U.S. Pat. No. 4,280,010, issued Jul. 21, 1981 to Erpenbach et al., discloses a continuous process for making alkyl acrylates free from ether by reacting a C.sub.1 -C.sub.4 -alkanol in a molar ratio of 1:1 to 1:2 in liquid phase at 80.degree. to 130.degree. C. under 100-760 mmHg in the presence of a catalyst. The process employs a single reaction zone and two distillation zones for separating the alkyl acrylate from unreacted alkanol and ether by-product.
U.S. Pat. No. 4,814,493, issued Mar. 21, 1989 to Dougherty et al., teaches a process for the production of an n-butyl acrylate by reaction of n-butanol with acrylic acid in the presence of an esterification catalyst and soluble manganese or cerium. The system for carrying out the process includes a reactor from which a butyl acrylate reaction product is sent to a finishing tower wherein the reaction product is separated into a pure butyl acrylate stream, a volatiles stream a portion of which is sent to a butanol recovery tower, and a residue stream which is recycled to the reactor. A butanol stream from the butanol recovery tower is recycled to the reactor, and a residue stream from such tower is removed from the system.
South African Patent No. 9704628 issued Mar. 25, 1998, discloses a process wherein acrylic acid (HAcA) and n-butanol (BuOH) are reacted in two reactors in series, and the product separated in two distillation columns to produce a stream comprising butyl acrylate (BuAcA), dibutyl ether (DBE), butyl acetate (BuAc), and BuOH. Such stream is further separated in a splitter distillation column to provide an overhead fraction containing DBE, BuAc, and BuOH, and a bottoms fraction containing BuAcA and heavy ends components, e.g., low molecular weight polymers of HAcA, and/or BuAcA, and Michael addition products ("heavies"). The overhead fraction from the splitter column is subjected to further distillation in the presence of water to separate BuOH and BuAcA from lights containing DBE and BuAc, with the BuOH and BuAcA being recycled to either or both reactors and the lights being sent to waste treatment, while the bottoms fraction from the splitter distillation is rectified in a butyl acrylate distillation column to separate BuAcA product from heavies which are recycled to either or both reactors.